I have finally finished a Freeradius based usage limiter with a PHP frontend for paypal payments for use with MT. Users can signup, login and buy Gigs, top up etc from a PHP interface and paypal and mysql database. The radius server can take any data limit and have a monthly limit and a top up bank. Oh and it dosen't use rlm_sqlcounter
It uses dynamic encrypted paypal buttons. The backend is secure and only adds credit once payment is completed.
It has taken me goddamn ages to develop this so I can offer it for sale if anyone is interested contact me here.. or at turboweb.org